Calcium ion is essential for the body, and the concentration of intracellular Ca2+ constituting the body is as extremely low as 10−7M, which is 1 to 10,000 relative to the extracellular concentration. When the cell is stimulated, intracellular Ca2+ increases to generate Ca2+ wave that produces slow intracellular Ca2+ oscillation, and induces physiological function.
SOCE (store-operated calcium entry) is also called capacitive calcium entry, which is a mechanism that causes extracellular influx of Ca2+ for replenishment of depleted intracellular Ca2+ stores, and important for long-term sustainability of intracellular Ca2+ signals.
SOCE is measured as Icrac (calcium release-activated calcium-selective current). It has been clarified that SOCE and Icrac channel are defective in the T cells of patients with severe combined immunodeficiency (SCID). Furthermore, it has also been clarified that a protein called STIM (stromal interaction molecule) senses depletion of Ca2+ in the endoplasmic reticulum, passes the information to the cellular membrane, and activates CRACM (calcium release-activated calcium modulator) (Orai) located in the cellular membrane and forms Icrac channel pore.
Extracellular stimulus is recognized by a receptor on the cellular membrane, the information thereof activates PLC (phospholipase C) via G protein and hydrolyzes PIP2 (phosphatidylinositol bisphosphate), which is an inositolphospholipid in the cellular membrane, and produces diacylglycerol and IP3 (inositol trisphosphate). Diacylglycerol activates protein kinase C and phosphorylates protein, causing various physiological phenomena. IP3 acts on IP3 receptor to cause release of Ca2+. The present inventors have found an IP3 receptor molecule in mutant mouse, and successfully determined all base sequences of the membrane protein (non-patent document 1). In addition, they have clarified that the IP3 receptor localizes in the endoplasmic reticulum, and this is the calcium channel (non-patent documents 1-5). Furthermore, the present inventors have clarified that the IP3 receptor is the molecule involved in development and differentiation, neural plasticity and various signal transduction (non-patent documents 6-11). In addition, they have clarified that the IP3 receptor is also bound to the Ca2+ channel on the cell membrane surface (non-patent document 12).
2-Aminoethyl diphenylborinate (2-APB: C6H5B (OCH2CH2NH2)C6H5) has been internationally recognized as an IP3 receptor inhibitor, and is sold from Sigma. It decreases intracellular calcium concentration by inhibiting SOCE. The present inventors have synthesized and found compounds that control intracellular calcium concentration (patent document 1, patent document 2, Japanese patent application No. 2008-028152).
It has been clarified that the causes of intractable diseases such as Alzheimer's disease, Parkinson's disease, Celiac disease, cataract, mad cow disease, congenital lamellar ichthyosis, congenital hemostatic disorder and the like are based on the abnormal cross-linking reaction of proteins (non-patent document 13, non-patent document 14). In addition, it has also been clarified that the cause of Huntington's disease is abnormal aggregation of polyglutamine (non-patent document 15).
Transglutaminase is an enzyme activated by the presence of Ca2+, and its involvement in neurological diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease and the like has recently been known. Therefore, novel inhibitors thereof are considered to be effective as therapeutic drugs for the diseases (non-patent document 16, non-patent document 17). A reaction forming an isopeptide bond by deammoniation of an amide group of glutamine and an amino group of lysine is the main reaction of protein cross-linking. The mechanism by which an inhibitor of enzyme transglutaminase causing the reaction is effective for the aforementioned neurological diseases has been clarified (non-patent document 19). As a basis, while many studies have been made based on the above to develop inhibitors of transglutaminase as therapeutic drugs for intractable diseases such as Alzheimer's disease, Huntington's disease, Parkinson's disease and the like (non-patent documents 17-23), a boron compound having a transglutaminase inhibitory activity has not been reported heretofore.